Refugees Attacked as They Flee Krajina Area : Balkans: Serbs form the largest flight of humanity in four years of warfare. They jam roads for miles.

ZAGREB, Croatia — In the largest flight of humanity in four years of Balkan bloodshed, a river of refugees Tuesday poured from the conquered Krajina region of Croatia--and many of them came under new attack.

Trapped by advancing armies, tens of thousands of Serb men, women and children on tractors and in horse-drawn carts desperately sought refuge outside a U.N. compound or simply jammed roads awaiting relief.

Epic scenes were unfolding for hundreds of miles across the former Yugoslav federation, from the Krajina southeast of Zagreb, eastward across northern Bosnia-Herzegovina to Serbia. Angry and anguished Serbs fled a victorious Croatian military, which had recaptured the Krajina in a weekend rout that ended the separatist rebels' vision of a Greater Serbia homeland.

More than 120,000 Serbs were moving from Croatia, the United Nations said, and officials estimated that the number could reach 200,000.

Relief workers, struggling to get water, fuel or basic shelter to the masses of displaced people, warned of a catastrophic humanitarian crisis.

"[There is] an endless river of refugees," Amanda Williamson, an official with the International Committee of the Red Cross, said in an interview in Zagreb, the Croatian capital. "People are in a state of panic and fear. Some can't move. People are wounded. . . . The authorities are just overwhelmed by the sheer . . . numbers."

Many of the refugees were blocked as they fled, caught between the Croatian army advancing from the north and the newly triumphant Bosnian government army from the south. About 30,000 refugees were reported trapped near the town of Topusko, 40 miles south of Zagreb, and at least that many 10 miles to the northeast at Glina.

The Bosnian government army, fresh from its success in breaking the siege of the U.N.-designated "safe area" of Bihac, torched six Bosnian Serb villages, U.N. officials said, and at the Croatian border with Bosnia prevented many of the refugees from crossing.

U.N. officials also said refugees were shelled by the Croatian army at the border town of Dvor; there was heavy small-arms fire and shelling overnight in the Glina area. Shelling was also reported near Topusko.

Yasushi Akashi, the U.N. special envoy in the Balkans, said he had reports of "indiscriminate shooting" of refugees. Casualties were reported but no number was given.

Pockets of Croatian Serb resistance were reported in the area, and armed fighters were among the fleeing refugees.

Red Cross and U.N. officials implored the Croatian and Bosnian government armies to distinguish between combatants and civilians caught in the cross-fire. Late Tuesday, a cease-fire agreement was reportedly reached, and Croatian officials announced the surrender of at least 4,000 Krajina Serbs.

The United Nations did not immediately confirm that a surrender agreement had been reached; previous ones have fallen apart. Milan Martic, the leader of the Croatian Serbs, who had not been seen in public since the Croatian offensive began, appeared on Bosnian Serb television to urge his soldiers to fight on.

The Croatian offensive took a heavy toll on many towns and villages in the Krajina, damage that was largely undocumented before Tuesday because the area had been off-limits to journalists. The Croatian government allowed the news media to pass through central Krajina on Tuesday en route to Bihac, in neighboring Bosnia.

In Slunj, an important military outpost for the Krajina Serb rebels, buildings were gutted, shops looted, homes destroyed and vehicles overturned. Outside of town, fires burned throughout the night in some homes.

Many villages suffered less damage, but windows in houses were shot out, and outside walls pocked with bullet holes.

In contrast, however, to the "ethnic cleansing" of Bosnian Muslims by Bosnian Serbs last month in the Bosnian enclaves of Srebrenica and Zepa, there were no immediate reports of women being raped or men being summarily executed.

For the most part, the Serbian civilians and many of the fighters seemed to have fled well ahead of the advancing Croatian forces.

While the Croats are eager to evict the Serbs from Croatian territory, neither the Bosnians nor the leaders of Serbia proper are eager to receive them. The Muslim-led but secular Bosnian government fears that the Krajina fighters will be incorporated into the Bosnian Serb army, which, like the Krajina Serb force, is fighting to conquer a Serbian homeland.

And Serbian President Slobodan Milosevic is reluctant to be overrun by refugees who are angry at him for failing to help save the Krajina. Milosevic is the original inspiration to the separatist Serbs, but he has shown little interest in assisting the Krajina Serbs in their war.

The depth of the betrayal felt by his onetime proteges was underscored Tuesday in an open letter from Bosnian Serb leader Radovan Karadzic. In unusually strong language, Karadzic accused Milosevic of selling out the Serbs in the interest of improving his international standing.